Wave Height and Horizon Dip

A mariner who takes the height of the sun or a star to find his position at sea, must correct his observation for horizon dip. Throughout history, dip values have been tabulated based on the idealized assumption of a perfectly flat sea. Literature on wave height correction for dip is scarce, especially in the Western part of the world and suggested procedures are often conflicting or incorrect. We investigate the effect of wave height on the apparent horizon for realistic wave height distributions by optical ray tracing methods and show that there are two eye height corrections: one representing the apparent rise of the horizon itself and the second when sights are selectively taken from wave crests. Tables and formulas for dip and horizon distance taking wave height into account are presented. Copyright © 2015 Institute of Navigation.